Hartmann S, Agostinelli C, Klapper W, Korkolopoulou P, Koch K, Marafioti T, Piccaluga P P, Patsouris E, Pileri S & Hansmann M‐L 
(2011) Histopathology 59, 1173–1182 
Revising the historical collection of epithelioid cell‐rich lymphomas of the Kiel Lymph Node Registry: what is Lennert’s lymphoma nowadays?

Aims:  Lennert’s lymphoma is a rare variant of peripheral T‐cell lymphoma (PTCL) not otherwise specified (NOS). The aim of this study was to further characterize this tumour.

Methods and results:  Historical material of 97 lymphomas with a high content of epithelioid cells, collected at the Kiel Lymph Node Registry were reviewed, by applying immunohistochemistry and current diagnostic criteria. Among all cases revised, various B‐cell lymphoma entities (25 cases), Hodgkin lymphomas (21 cases) and PTCL subtypes (48 cases) could be identified. A distinctive subgroup of eight PTCLs was found that were regarded as genuine Lennert’s lymphomas. These cases were characterized by mild atypia, a non‐activated cytotoxic phenotype [TIA1 cytotoxic granule‐associated RNA binding protein (TIA1)‐positive⁺ and granzyme B‐negative], and a substantial lack of follicular T‐helper (T_FH) cell markers. Among the other PTCLs, including angioimmunoblastic T‐cell lymphoma and PTCL NOS, many cases with positivity for more than three T_FH cell‐associated molecules were recorded.

Conclusions:  Our study shows that, according to current criteria, Lennert’s lymphoma is a rare but distinctive entity among epithelioid cell‐rich lymphomas, differing on grounds of morphology and immunophenotype from other PTCL subtypes. An additional finding is the broad morphological spectrum of epithelioid‐cell rich PTCLs showing a T_FH cell phenotype.